Nine factors account for more than a third of the seven million cancer deaths a year which could be avoided. Reducing smoking and alcohol and eating more fruit and vegetables are the most important factors but little effort is going into promoting their life-saving effects, researchers say in the Lancet medical journal.
Scientists from the US, Australia and New Zealand say the obsession with curing cancer has prevented progress in the war against the disease whose incidence is growing. Although screening and treatment are increasingly effective in reducing the toll, their benefits are limited by cost and difficulty of access to them in many countries.
"Advances in cancer treatment have not been as effective as those for other chronic diseases," they say. "Primary prevention through lifestyle and environmental interventions remains the main way to reduce the burden of cancer."
Smoking is the biggest killer, causing 21 per cent of cancer deaths worldwide. Alcohol use and low fruit and vegetable consumption are the next most lethal, each accounting for 5 per cent of cancer deaths. Smoking mainly causes lung cancer, accounting for 70 per cent of the 1.2 million deaths from the disease. But it also causes eight other cancers: mouth (42 per cent of deaths), oesophagus (42 per cent), stomach (13 per cent), liver (14 per cent), pancreas (22 per cent), cervix (2 per cent), bladder (28 per cent) and leukaemia (9 per cent).
Other risk factors include being overweight and obesity, which account for 11 per cent of colon cancer deaths and 40 per cent of deaths from cancer of the uterus. Physical inactivity increases the risk of breast cancer, accounting for 10 per cent of all deaths from the disease and of colon cancer (15 per cent).
Low fruit and vegetable consumption is a risk factor for cancers of the oesophagus (18 per cent of deaths), stomach (18 per cent), colon (2 per cent) and lung (11 per cent).
Unsafe sex - without a condom - can transmit the papilloma virus which causes all cases of cervical cancer. Cervical cancer causes 234,000 deaths worldwide, more than 90 per cent of them in low and middle-income countries.
Urban air pollution, worse in the developing world, and indoor smoke from open fires and solid-fuel cookers used with inadequate ventilation increase the risk of lung cancer.
The common practice of re-using needles for medical injections in the developing world transmits hepatitis and other viruses that cause liver cancer.
Majid Ezzati, of the Harvard School of Public Health who led the study, said: "Primary prevention through lifestyle and environmental interventions remains the main route for reducing the global cancer burden.
"Reduction of exposure to well-known behavioural and environmental risk factors would prevent a substantial proportion of deaths from cancer."
* A blood test to assess the risk of developing cancer could be available in the next decade.
Professor Karol Sikora, from Imperial College, London, and Hammersmith Hospital, also said that, in 20 years, cancer would probably be a controllable disease.
What to look out for
SMOKING
Linked to a large number of cancers including of the mouth, oesophagus, stomach, liver, pancreas, cervix, bladder, lungs and bone marrow
ALCOHOL
Causes cancers of the mouth, oesophagus, liver and breast
OBESITY
Causes cancers of the uterus, colon and breast
PHYSICAL INACTIVITY
Causes breast and colon cancer
UNSAFE SEX
Causes cancer of the cervix
URBAN AIR POLLUTION
Causes lung cancer
SMOKE FROM FUELS
Causes lung cancer
CONTAMINATED MEDICAL INJECTIONS
Causes cancer of the liver
LOW VEGETABLE AND FRUIT CONSUMPTION
Causes cancers of the colon, stomach, lungs and oesophagus
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